Link - wait for next BPM change after calling set

This gives chance for link to register the new bpm and then report it back so it can be used in the next instruction. If no new BPM is received after 100ms, execution continues anyway.

Author: samaaron

app/server/ruby/lib/sonicpi/tau_api.rb

@@ -21,6 +21,8 @@ class TauAPI
     attr_reader :booted
 
     def initialize(ports, handlers)
+      @incoming_tempo_change_cv = ConditionVariable.new
+      @incoming_tempo_change_mut = Mutex.new
       @tau_api_events = IncomingEvents.new
       @client_id = @tau_api_events.gensym("RubyTauAPI")
       @osc_cues_port = ports[:osc_cues_port]
@@ -40,6 +42,7 @@ def initialize(ports, handlers)
       @link_time_micros = nil
       @local_time_micros = nil
       @link_time_delta_micros_prom = Promise.new
+
       Thread.new do
         initialize_link_info!
       end
@@ -125,7 +128,13 @@ def link_get_beat_at_clock_time(clock_time, quantum = 4)
     end
 
     def link_set_bpm_at_clock_time!(bpm, clock_time)
-      @tau_comms.send_ts(clock_time, "/link-set-tempo", bpm.to_f)
+      res = @tau_comms.send_ts(clock_time, "/link-set-tempo", bpm.to_f)
+
+      # Wait for a max of 100ms for the next tempo change to come in...
+      @incoming_tempo_change_mut.synchronize do
+        @incoming_tempo_change_cv.wait(@incoming_tempo_change_mut, 0.1)
+      end
+      res
     end
 
     def link_disable
@@ -190,6 +199,7 @@ def initialize_link_info!
 
     def add_incoming_api_handlers!
       @tau_comms.add_method("/link-tempo-change") do |args|
+        @incoming_tempo_change_cv.broadcast
         gui_id = args[0]
         tempo = args[1].to_f
         @tempo = tempo